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Supplemental cash flow information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Interest	$ 38.5	$ 19.8
Income taxes, net	72.8	64.9
Capital Leases	42.0	33.4
Restricted cash	92.7		$ 112.6
Cash and cash equivalents	314.2		614.3
Cash, Cash Equivalents, and Restricted Cash	406.9	$ 327.5	726.9	$ 239.0
Cash from Short Term Borrowings
Condensed Cash Flow Statements, Captions [Line Items]
Restricted cash	11.3		27.0
Cash Held From Customers
Condensed Cash Flow Statements, Captions [Line Items]
Restricted cash	46.9		74.7
Deposits liability
Condensed Cash Flow Statements, Captions [Line Items]
Restricted cash	$ 34.5		$ 10.9